1. Field of the Invention
This invention relates to magnetic recording disk drives, and more particularly to a system and method for determining contact of the read/write head or the head carrier with the disk.
2. Description of the Related Art
Magnetic recording hard disk drives use a read/write transducer or head mounted on a head carrier for reading and/or writing data to the disk. The head carrier is typically an air-bearing slider attached to an actuator arm by a suspension and positioned very close to the disk surface by the suspension. There are typically a stack of disks in the disk drive with a slider-suspension assembly associated with each disk surface in the stack.
The separation between the head and the disk surface is called the fly height. The slider has a disk-facing air-bearing surface (ABS) that causes the slider to ride on a cushion or bearing of air generated by rotation of the disk. The slider is attached to a flexure on the suspension and the suspension includes a load beam that applies a load force to the slider to counteract the air-bearing force while permitting the slider to “pitch” and “roll”. The flying dynamics of the slider and thus the fly height are influenced by factors such as the rotation speed of the disk, the aerodynamic shape of the slider's ABS, the load force applied to the slider by the suspension, and the pitch and roll torques applied to the slider by the suspension.
Disk drives are susceptible to failure of the slider-disk interface which can result in a head “crash” during operation. This may result in loss of data or complete failure of the disk drive. Because head crashes can not always be prevented, it is important that contact of the slider with the disk, or contact of the read or write head with the disk, collectively called head-disk contact (HDC), be detectable or predictable. In the event of an impending head crash, as judged by HDC detection circuitry, a warning should be provided so that critical data can be backed up either manually or automatically. One type of HDC warning system can be implemented in disk drives that use SMART (Self-Monitoring Analysis and Reporting Technology).
Disk drives have been proposed that use a fly-height actuator for changing the spacing between the head and the disk surface. One type of fly-height actuator is a thermal actuator with an electrically-resistive heater located on the slider near the head. When power is applied to the heater the heater expands and causes the head to “protrude” and thus move closer to the disk surface. Other fly-height actuators for moving the head relative to the slider include electrostatic microactuators and piezoelectric actuators. Another type of fly-height actuator, also based on thermal, electrostatic or piezoelectric techniques, changes the head-disk spacing by altering the air-flow or the shape of the slider's ABS. In disk drives that have a fly-height actuator it is important to be able to determine the onset of HDC so that the fly-height actuator can be accurately controlled.
A method for determining HDC is also important during the design and testing of disk drive components, in particular the slider ABS and the fly-height actuator, with the use of a head-disk tester.
For all of these reasons a system and method is needed for reliable determination of HDC in a magnetic recording disk drive.